An Age-Old Question

We've all seen robins catching earthworms on a lawn. They are amazingly successful at it. Ornithologists (and others) have long wondered whether they are keying in on the worms by sight or by hearing, and they seem to be divided on the answer. Is the bird in this image using it's sight to locate a worm or is it listening? It appears it could be using either.

I personally believe they can hear the worms (and some studies support this). I have a couple of reasons why I believe this. Have you ever watched a movie where the camera perspective is a flyover of a city? Directly below, you can see the individual city streets, but as you look further into the distance, you cannot see any streets because so many buildings are in the way. From the perspective of a robin, the lawn is pretty much the same kind of situation. It may be able to see the dirt directly around it, but it cannot see the dirt only a few feet away because too much grass is in the way. Hearing, however, would not be impeded in this type of scenario. 

I know. That isn't completely convincing, but it does still leave open the possibility that they use hearing to key in on worms. One scientist described what a worm sounds like as similar to a person walking through gravel. This particular robin had some babies to feed and was piling up pieces of worm to take to them.

This is what really convinces me, though, and it doesn't actually involve a robin, but rather, a starling. I was watching a starling parent and it's chick one day that were feeding in the mulch around some flower beds. I could see them very well because I was looking through a window which kept them from being frightened away and yet they were only a couple of feet away. The parent and chick were both hunting for grubs underneath the mulch. The chick would scratch in the mulch and come up with nothing most of the time. The parent, on the other hand, found a grub every time it scratched through the mulch. I was amazed as time after time, it would hop to a spot, scratch a little bit, and produce a big fat grub. The bird could not have been using it's sight. It was only after digging down with it's beak that the grub would appear. So, I had to conclude that it was hearing the grubs under the mulch and that the chick was also learning how to locate grubs.

I was surprised by the male Red-bellied Woodpecker flying in and landing where the robin was on the lawn. I think it was hoping the robin would drop the worm it had in it's beak. Red-bellied Woodpeckers probably do not have the same ability as the robin and was resorting to thievery. But, he wasn't early enough to get the worm.